It is always good to add a favicon to your website. The favicon is a 16x16 image file in the .Ico format. This image is the one you see next to the URL bar, next to the title of the page on an opened tab and is also visible on your bookmarks tab if you choose to bookmark a page. The favicon will help users quickly recognize your page in their browser without reading any text or directly viewing the page.
Don't use splash pages for your site unless required by law, and especially don't use a Flash intro. Most people just want to get to your content as quickly as possible, and don't care to look at useless splash pages. If you have some amusing content that you absolutely want visitors to see, integrate it into the homepage instead.
Testing your website in every browser available is a great way to ensure it works as you wish it to for every visitor. Your content may show up fine in online advertising questionnaire, but it may be unreadable or badly displayed in Chrome, Firefox or Safari. Therefore, you should check how all the pages of your website display in all the major browsers on the market, before turning your site live.
Test your website before it goes live. There's nothing worse then launching your new website and having to take it down right away due to bugs or other issues. Get a group of people together who are using different web browsers and computer platforms, and ask them to use a beta version of your website, writing down any issues they come across.
Use images wisely. Bitmap images do not tend to fare well for internet use, and some GIFs do not work well with lots of color. Image size is important as well, as larger images may make your viewers have to wait for them to download. Choose smaller images, and use them sparingly to make your site more manageable.
Never use pop-ups. Customers are turned off by the constant advertising pop-up ads represent. They'll be much more likely to leave your site out of annoyance if they are confronted with pop-ups. Stay away from these types of annoying ads, and your customers will be happier. If your webhost places their own popup ads on your website, it is time for you to change your webhost.
Be sure your website works both with and without the "www" prefix. Some people will type this in before they head to your site as a force of habit, and some may not. You should make sure that customers will be directed to your site either way, or you may have some confused people on your hands.
You will start seeing how things fit together when learning about website development. It starts by reading great tips like the ones here, then putting it all together. Use this information to make a great website.